In the related art, due to a reduction in the size of an electronic device or electric device, reductions in the size and the thickness of a component for an electronic/electric device such as a terminal including a connector or the like, a relay, a lead frame, or the like used in the electronic device, the electric device, or the like have been achieved. Therefore, as a material of the component for an electronic/electric device, a copper alloy having excellent spring properties, strength, and bending formability has been required. Particularly, as disclosed in Non-Patent Document 1, it is desirable for the copper alloy used in the component for an electronic/electric device such as a terminal including a connector or the like, a relay, a lead frame, or the like to have high proof stress.
As a copper alloy that is used for a component for an electronic/electric device such as a terminal including a connector or the like, a relay, a lead frame, or the like, the Cu—Mg alloy described in Non-Patent Document 2, the Cu—Mg—Zn—B alloy described in Patent Document 1, and the like have been developed.
With regard to the Cu—Mg based alloy, as is known from a Cu—Mg system phase diagram shown in FIG. 1, in the case where the amount of Mg is 3.3 at % or more, intermetallic compounds containing Cu and Mg can be precipitated by performing a solutionizing treatment and a precipitation treatment. That is, with regard to the Cu—Mg based alloy, relatively high electrical conductivity and strength can be achieved by precipitation hardening.
However, in the Cu—Mg-based alloy described in Non-Patent Document 2 and Patent Document 1, a large amount of coarse intermetallic compounds containing Cu and Mg as main components are dispersed in the matrix phase. Therefore, during bending working, these intermetallic compounds serve as starting points, and cracking and the like are likely to occur therefrom. As a result, there has been a problem in that the copper alloy cannot be formed into components for an electronic/electric device having complicated shapes.
Particularly, in components for an electronic/electric device which are used for commercial products such as mobile phones, personal computers, and the like, there is a demand for a reduction of size and weight, and a copper alloy for an electronic/electric device having both good strength and good bending formability is required. However, with regard to a precipitation hardening alloy such as the above-described Cu—Mg-based alloy, when strength and proof strength are improved by precipitation hardening, bending formability greatly degrades. Therefore, it has been impossible to form the copper alloy into a thin component for an electronic/electric device having a complicated shape.
Therefore, in Patent Document 2, a work hardening copper alloy of a Cu—Mg solid solution alloy supersaturated with Mg is proposed which is produced by rapidly cooling a Cu—Mg alloy after solutionizing.
This Cu—Mg alloy has excellent strength, electrical conductivity, and bendability and is particularly suitable as a material for the above-described components for an electronic/electric device.
Meanwhile, in recent years, the sizes and weights of electronic/electric devices have been further reduced. Here, with regard to a small-sized terminal that is used in an electronic/electric device having a reduced size and a reduced weight, from the viewpoint of the yield of a material, the material is bent so that the bending axis becomes a direction (Good Way: GW) perpendicular to a rolling direction, and the material is slightly deformed (bent) so that the bending axis becomes a direction (Bad Way: BW) parallel to the rolling direction. Thereby, the material is formed into the terminal, and the spring properties are ensured due to the material strength TSTD measured by a tensile test in the direction of BW. Therefore, an excellent bending formability in the direction of GW and a high strength in the direction of BW are obtained.